In a color photograph, as is well known, couplers react with the oxidation product of an aromatic primary amine color developing agent, which is formed by developing a silver halide color photographic light-sensitive material, to thereby form a color image composed of dyes such as indophenol, indoaniline, azomethine, phenoxazone, quinoneimine, phenazine and dyes similar therto. A color reproduction is generally carried out by a subtractive color process, and there are used silver halide emulsions spectrally sensitive to blue, green and red, and couplers for forming yellow, magenta and cyan dyes, which are complementary colors for blue, green and red, respectively. There are generally used as a yellow dye forming coupler, the compounds having an active methylene group; as a magenta dye-forming coupler, a pyrazolone type, pyrazolobenzimidazole type, pyrazolotriazole type or indazolone type compounds; and as a cyan dye-forming coupler, a phenol type or naphthol type compounds.
Each of these couplers generally requires four silver atoms in order to form one molecule of a dye. Dut to the shortage of silver resources, silver-saving type couplers have been proposed; for example, the technique is disclosed in Japanese Patent Examined Publication No. 13576/1974 in which there is used a coupler having a splitting off group introduced to its active site for forming one molecule of a dye with two silver atoms, the so-called two equivalent coupler. This method enables to reduce by half the amount of silver required for a conventional four equivalent type coupler, so that two equivalent couplers have been widely used in recent years.
Though the known two equivalent couplers are effective to some extent, there are still demanded more improvements of the characteristics, particularly in the color formability. The coupler have been demanded to be more reactive to meet the recently prevailing requirements for higher sensitivity and higher image quality as well as saving of processing time. It is possible to increase the sensitivity of a light-sensitive material by raising the reactivity of a coupler to the oxidation product of a color developing agent. Further, more reactive coupler makes it possible to reduce the amounts of the coupler and silver halide without decreasing the sensitivity. As the result, the thickness of the light-sensitive material is reduced and the scattering of an incident light is decreased, resulting in improvement of the sharpness. In the negative and reversal light-sensitive materials, a blue-sensitive layer is provided nearest a light-incident side, so that reducing the thickness of the blue-sensitive layer is the most effective. Therefore, the development of especially high reactive yellow couplers has been expected.
On the other hand, in the developing process, benzyl alcohol is added to a conventional color developing solution to increase the color forming efficiency of a light-sensitive material. Benzyl alcohol is lable to cause an environmental pollution problem such as increase of a B.O.D. (biological oxygen demand) value. Accordingly, it is necessary to add less amount of benzyl alcohol in a color developing process. However, if the photographic material containing a conventional yellow coupler is developed in a processing solution containing less amount of bezyl alcohol especially in a shorter developing time, the density of a developed color image is lowered significantly. Thus, the development of a yellow coupler having a sufficient color formability even in developing with less amount of benzyl alcohol has also been expected. The conventional four-equivalent and two equivalent couplers cannot necessarily solve the above problems. On the contrary, two equivalent yellow couplers having a non-diffusible group and an aryloxy group as a splitting off group have been noted as ones capable of solving the above problems. The examples of the two-equivalent yellow couplers having a non-diffusible group include aryloxy-splitting off type two equivalent yellow couplers having a sulfamoyl or acylamino group disclosed in U.S. Pat. No. 3,644,498; ones having an alkoxycarbonyl group disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 174839/1984; and an alkyl or arylsulfamoyl group disclosed in Japanese Patent O.P.I. Publication No. 69653/1985. These couplers are known to be significantly improved in a color forming efficiency particularly when there is introduced into a para-position of an aryloxy group thereof, an electron attractive group such as a sulfonyl group, a sulfamoyl group, a carbamoyl group, an acyl group, a formyl group, a nitro group and a cyano group. These couplers have a poor solubility in a high boiling solvent due to a non-diffusible group and a low dispersing stability in a silver halide emulsion. Obviously, this will cause a problem particularly when the amount of a high boiling solvent is reduced for a thinner layer which has been prevailing in recent years. Further, most of the couplers disclosed in the above patent publications are still not satisfactory in a coupling reactivity and a density of a formed color image, so that the coating amount thereof needs to be increased.
As the yellow coupler capable of meeting demands for improving both the solubility in a high boiling solvent and the high color formability, aryloxy-splitting off type two equivalent yellow couplers having a sulfonamido group as a nondiffusible group are described in U.S. Pat. No. 3,933,501. However, the couplers disclosed therein are pivaloylacetanilide yellow couplers having an inferior activity to benzoylacetanilide couplers, so that their color formability and solubility to solvents does not yet reach any satisfactory level. Japanese Patent O.P.I. Publication No. 43144/1988 describes yellow couplers having a sulfonamido group as a non-diffusible group, in which the solubility is improved by introducing a branched alkoxycarbonyl group into the para position to an oxygen atom of an aryloxy group. The couplers disclosed therein are pivaloylacetanilide couplers intended for improving an antifading property, and are unsatisfactory in color formability. Japanese Patent O.P.I. Publication No. 153955/1987 describes aryloxy-splitting off type two equivalent yellow couplers intended for improving both solubility and color formability by introducing a specific arylsulfonamido group. However, the arylsulfonamido group is inherently inferior in both solubility and dispersing stability in an emulsion, and the arylsulfonamido non-diffusible group of the couplers disclosed therein has a very complicated structure in order to improve the above matters. Thus, it is liable to increase the coupler's manufacturing processes, resulting in an increase in cost. Japanese Patent O.P.I. Publication No. 153954/1987 describes yellow couplers having a sulfonamido non-diffusible group and an aryloxy group having a cyano group in the para-position to the oxygen atom thereof. However, the majority of the couplers disclosed therein also are pivaloylacetanilide yellow couplers having an insufficient color formability level because of the above-mentioned reason.
Further, this publication also discloses benzoylacetanilide type aryloxy-splitting off two equivalent yellow couplers, however the aryloxy group in which a cyano group is merely introduced to the para-position is not enough to provide the sufficient activity and, therefore, these couplers have no sufficient color formability, either. The publication further discloses other yellow couplers having an aryloxy group with a cyano group introduced to the para-position and a chlorine atom to the ortho-position in order to raise the activity, however the color formability is still not sufficient. Moreover, the substituent introduced into the ortho-position results in reducing the coupler's solubility in a high boiling solvent.
U.S. Pat. No. 4,401,752, Japanese Patent O.P.I. Publication Nos. 228649/1984 and 250446/1987 describe that the color formability is further improved by introducing an electron attractive group, particularly a so-called polarizable group, to the ortho position of an aryloxy group. However, the couplers disclosed therein still have a poor solubility in a high boiling solvent and a low dispersion stability because of the above-mentioned reason.
On the other hand, it is proposed to improve a color formability by introducing a hydrophilic group into a non-diffusible group. For example, European Patent No. 0,073,636 describes that the color formability is improved by a non-diffusible group having on its terminal a hydroxyphenylsulfonyl group. However, the hydrophilic group introduced into the non-diffusible group reduces a dispersing stability of a coupler in an emulsion and further, the non-diffusible group becomes so complex as to result in increasing a manufacturing cost.